ACorrelated History of Earth
is a full-color educational wallchart documenting 4.5
billion years of earth's natural history. Each column is
a timeline from ancient times to recent. Included are
plate tectonic maps, mountain building events(orogenies),
major volcanic episodes, glacial epochs, all
known craters from asteroid and comet impacts,
over 100 classic fossil localities from around the world,
fossil Ranges of plants, invertebrates and vertebrate
lifeforms, and major extinction events as revealed by the
fossil record. Also evident on this chart are the
"cambrian "explosion" of animal phyla and
the juxtaposition of reptiles and mammals across the
Cretaceous/Tertiary(K/T) boundary. Hundreds of
illustrations add a striking visual dimension to the
data.

A Galactic Orbit
Model for Periodic Mass Extinction

New Theory Explains
Timing of Major Impacts and Extinction Events

Life on planet Earth has experienced 6 major and several minor
extinction events over the past 620 million years. Statistical
analyses suggest a periodic nature to these events. However, no
model has been able to elegantly explain the apparent
non-randomness in the data. A new astronomical model presented
here, the GalacticOrbit model, shows a much
stronger correlation with extinction and impact data (both
craters and extraterrestrial geochemical signatures in Earth
sediments) than previous models. It explains periodicity by
invoking a 186 million-year galactic orbital period
(corresponding to a galactic "year" for our solar
system) with three discreet zones of high extinction for every
trip around the galactic nucleus.

In recent years, two periodic extinction models have received
the most attention in the scientific community and the media. The
first is known as the Nemesis modeland the second
is the Galactic Plane transitmodel. Both involve a
perturbation of Oort cloud comets, resulting in comet showers to
the inner solar system. One or more of these comets then strike
the Earth, causing catastrophic environmental changes and mass
extinction of species.

The Nemesis model asserts that a somewhat massive solar
companion gravitationally disrupts the Oort cloud at perihelion
every 26 million years. However, such an object has not been
found in spite of searches. Furthermore, an object with the
necessary mass and orbital period is likely to have an unstable
orbit. Passing stars would probably have stripped it away from
our sun eons ago. The Galactic Plane transit model asserts
that our solar systems passage through the matter-rich
galactic plane every 32 million years provides sufficient
gravitational flux to disrupt Oort cloud comets. This idea is
similar to "disk stripping" of globular clusters
outer stars, also thought to occur due to passage through the
galactic plane.Both of these models fail the predictions test. A
group of extinctions should line up on 26 or 32 million year
intervals. No such grouping is observed in the fossil record,
although gaps of 26-32 million years are sometimes observed
between extinctions.

The periodic nature of impacts and extinctions is displayed in
detail on my educational map entitled:"A
Correlated History of the Universe" by Pan Terra
Inc. Notice the four largest probable impact events:(the K/T,
P/Tr, O/S, Stu/V boundaries) are evenly spaced by ~186 million
year intervals. The Galactic Orbit model implies that these four
events occurred when our solar system passed through the most
dangerous zone, or Zone-1. The impact/extinction data also
suggests 2 minor Zones, also causing extinctions with a 186
million year period (just like Zone-1). Zone-2 transit follows
Zone-1 transit by about 32 million years. Zone-3 follows Zone-2
by about 40 million years. After we get past Zone-3, there is a
relatively quiet gap of 114 million years until the solar system
returns to Zone-1.

An analogue to this model would be the annual meteor showers
seen from Earth. The comet debris trails that cause the showers
are basically fixed with respect to earth's orbit. We hit them
the same time every year like clockwork as we orbit the sun. On
the galactic scale, the time required for our solar system to
make a lap around the galactic nucleus has been estimated to be
in the range of 200-250 million years. The Galactic Orbit model
suggests that 186 million years might be the effective period for
our solar system. Perhaps we encounter stationary zones or
features (relative to our galactic orbit) where gravitational
flux or possibly shockwaves cause Oort cloud comets to venture
into the inner solar system in large numbers.

Some candidate agents include spiral arms, giant molecular
clouds, interactions between our galaxy and others, rapid bursts
of star formation, supernovae generating shockwaves, etc. There
may be multiple causative agents in this model. The 186 million
year period and the three dangerous zones are the key ideas.The
Galactic Orbit model might explain why the 26-32 million year
periodicity ideas became popular. What researchers may actually
have been detecting with statistical analyses are the stagger
times (or sums and multiples thereof) between the three galactic
danger zones.

Some predictions of the Galactic Orbit model can be tested. We
should see a repeating pattern of Zone-1, 32 million year gap,
Zone-2, 40 million year gap, Zone-3, 114 million year gap, then
back to Zone-1. Research indicates a strong correlation between
the predictions, the impact data and the extinction record. Also
successfully predicted are the big gaps without mass extinction,
which the other theories cant explain. Curiously, the
Earths magnetic field seems to stabilize for extended
periods during this long 114 million year quiescent gap, as
suggested by the Kiaman superchron preceeding the P/Tr and the
Cretaceous magnetic quiet zone preceeding the K/T.

The impact and extinction data for Earth is a complex natural
history puzzle. The Galactic Orbit model succeeds in
predicting all of the major impact/extinction events as well as
the long, relatively quiet times in between. One additional
prediction is for an extraterrestrial signature to be found in
rocks deposited during the Silurian/Devonian boundary interval.
All of the other predicted times have strong statistical
correlation with mass extinction, craters, and/or
extraterrestrial geochemical signatures of various types. Events
like the Jurassic/Cretaceous boundary (where craters and moderate
extinction are present but the timing does not fit with the
predictions of the model) would be caused by other culprits
including random comets, random large asteroids, random
gravitational effects from passing massive bodies or
shockwaves/radiation from proximal exploding bodies(supernovae).

The question arises, where are we are now? Our solar system
will hit the Zone-3 peak in about 7 million years. Given the
cosmic scales and dating uncertainties, one might say our foot is
at the door of Zone-3. In terms of galactic geography, we are
beginning to enter the inner part of the Orion spiral arm. The
last time we were "here", an 80km diameter crater
(Puchezh-Katunki in Russia) greeted Earth and some of the
dinosaur groups of that time had a noticeably bad year. On the
Zone-3 visit previous to that (186 million years earlier),
multiple craters and late Devonian mass extinctions were the
result, perhaps the fourth or fifth worst extinction known from
the fossil record. The Galactic Orbit model predicts 365 million
years ago for the danger peak. We actually have evidence for two
discreet extinction events during this interval, the
Frasnian/Fammenian at ~367mya and the Devonian/Carboniferous at
~360mya. The good news is that the ultimate killer, Zone-1, is
still 120 million years away and may be correlated to our solar
system passing through the Crux spiral arm of the Milky Way.

If this model or something like it is shown to be useful, it
might lead astronomers to examine our solar systems local
neighborhood in more detail, along with a closer look at the
long-period comet data. It might be possible to determine favored
directions from which comets might be emanating and focus more
observational assets toward those regions.

In the course of my research, I occasionally discover
something that merits additional publishing efforts to properly
disseminate the discovery through the scientific community. I am
seeking collaboration with interested parties who publish in the
area of galactic dynamics, with the goal of refining and
publishing the Galactic Orbit model in an appropriate,
peer-reviewed publication.